/*
 * Copyright (c) 2016 AsyncHttpClient Project. All rights reserved.
 *
 * This program is licensed to you under the Apache License Version 2.0,
 * and you may not use this file except in compliance with the Apache License Version 2.0.
 * You may obtain a copy of the Apache License Version 2.0 at
 *     http://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the Apache License Version 2.0 is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
 */
package org.asynchttpclient.util;

import java.util.BitSet;

public final class Utf8UrlEncoder {

    // see http://tools.ietf.org/html/rfc3986#section-3.4
    // ALPHA / DIGIT / "-" / "." / "_" / "~"
    private static final BitSet RFC3986_UNRESERVED_CHARS = new BitSet();
    static {
        for (int i = 'a'; i <= 'z'; ++i) {
            RFC3986_UNRESERVED_CHARS.set(i);
        }
        for (int i = 'A'; i <= 'Z'; ++i) {
            RFC3986_UNRESERVED_CHARS.set(i);
        }
        for (int i = '0'; i <= '9'; ++i) {
            RFC3986_UNRESERVED_CHARS.set(i);
        }
        RFC3986_UNRESERVED_CHARS.set('-');
        RFC3986_UNRESERVED_CHARS.set('.');
        RFC3986_UNRESERVED_CHARS.set('_');
        RFC3986_UNRESERVED_CHARS.set('~');
    }

    // gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
    private static final BitSet RFC3986_GENDELIM_CHARS = new BitSet();
    static {
        RFC3986_GENDELIM_CHARS.set(':');
        RFC3986_GENDELIM_CHARS.set('/');
        RFC3986_GENDELIM_CHARS.set('?');
        RFC3986_GENDELIM_CHARS.set('#');
        RFC3986_GENDELIM_CHARS.set('[');
        RFC3986_GENDELIM_CHARS.set(']');
        RFC3986_GENDELIM_CHARS.set('@');
    }

    // "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="
    private static final BitSet RFC3986_SUBDELIM_CHARS = new BitSet();
    static {
        RFC3986_SUBDELIM_CHARS.set('!');
        RFC3986_SUBDELIM_CHARS.set('$');
        RFC3986_SUBDELIM_CHARS.set('&');
        RFC3986_SUBDELIM_CHARS.set('\'');
        RFC3986_SUBDELIM_CHARS.set('(');
        RFC3986_SUBDELIM_CHARS.set(')');
        RFC3986_SUBDELIM_CHARS.set('*');
        RFC3986_SUBDELIM_CHARS.set('+');
        RFC3986_SUBDELIM_CHARS.set(',');
        RFC3986_SUBDELIM_CHARS.set(';');
        RFC3986_SUBDELIM_CHARS.set('=');
    }

    // gen-delims / sub-delims
    private static final BitSet RFC3986_RESERVED_CHARS = new BitSet();
    static {
        RFC3986_RESERVED_CHARS.or(RFC3986_GENDELIM_CHARS);
        RFC3986_RESERVED_CHARS.or(RFC3986_SUBDELIM_CHARS);
    }

    // unreserved / pct-encoded / sub-delims / ":" / "@"
    private static final BitSet RFC3986_PCHARS = new BitSet();
    static {
        RFC3986_PCHARS.or(RFC3986_UNRESERVED_CHARS);
        RFC3986_PCHARS.or(RFC3986_SUBDELIM_CHARS);
        RFC3986_PCHARS.set(':');
        RFC3986_PCHARS.set('@');
    }

    private static final BitSet BUILT_PATH_UNTOUCHED_CHARS = new BitSet();
    static {
        BUILT_PATH_UNTOUCHED_CHARS.or(RFC3986_PCHARS);
        BUILT_PATH_UNTOUCHED_CHARS.set('%');
        BUILT_PATH_UNTOUCHED_CHARS.set('/');
    }

    private static final BitSet BUILT_QUERY_UNTOUCHED_CHARS = new BitSet();
    static {
        BUILT_QUERY_UNTOUCHED_CHARS.or(RFC3986_PCHARS);
        BUILT_QUERY_UNTOUCHED_CHARS.set('%');
        BUILT_QUERY_UNTOUCHED_CHARS.set('/');
        BUILT_QUERY_UNTOUCHED_CHARS.set('?');
    }

    // http://www.w3.org/TR/html5/forms.html#application/x-www-form-urlencoded-encoding-algorithm
    private static final BitSet FORM_URL_ENCODED_SAFE_CHARS = new BitSet();
    static {
        for (int i = 'a'; i <= 'z'; ++i) {
            FORM_URL_ENCODED_SAFE_CHARS.set(i);
        }
        for (int i = 'A'; i <= 'Z'; ++i) {
            FORM_URL_ENCODED_SAFE_CHARS.set(i);
        }
        for (int i = '0'; i <= '9'; ++i) {
            FORM_URL_ENCODED_SAFE_CHARS.set(i);
        }

        FORM_URL_ENCODED_SAFE_CHARS.set('-');
        FORM_URL_ENCODED_SAFE_CHARS.set('.');
        FORM_URL_ENCODED_SAFE_CHARS.set('_');
        FORM_URL_ENCODED_SAFE_CHARS.set('*');
    }

    private static final char[] HEX = "0123456789ABCDEF".toCharArray();

    private Utf8UrlEncoder() {
    }

    public static String encodePath(String input) {
        StringBuilder sb = lazyAppendEncoded(null, input, BUILT_PATH_UNTOUCHED_CHARS, false);
        return sb == null ? input : sb.toString();
    }

    public static StringBuilder encodeAndAppendQuery(StringBuilder sb, String query) {
        return appendEncoded(sb, query, BUILT_QUERY_UNTOUCHED_CHARS, false);
    }

    public static String encodeQueryElement(String input) {
        StringBuilder sb = new StringBuilder(input.length() + 6);
        encodeAndAppendQueryElement(sb, input);
        return sb.toString();
    }

    public static StringBuilder encodeAndAppendQueryElement(StringBuilder sb, CharSequence input) {
        return appendEncoded(sb, input, FORM_URL_ENCODED_SAFE_CHARS, false);
    }

    public static StringBuilder encodeAndAppendFormElement(StringBuilder sb, CharSequence input) {
        return appendEncoded(sb, input, FORM_URL_ENCODED_SAFE_CHARS, true);
    }

    public static String percentEncodeQueryElement(String input) {
        if (input == null) {
            return null;
        }
        StringBuilder sb = new StringBuilder(input.length() + 6);
        encodeAndAppendPercentEncoded(sb, input);
        return sb.toString();
    }

    public static StringBuilder encodeAndAppendPercentEncoded(StringBuilder sb, CharSequence input) {
        return appendEncoded(sb, input, RFC3986_UNRESERVED_CHARS, false);
    }

    private static StringBuilder lazyInitStringBuilder(CharSequence input, int firstNonUsAsciiPosition) {
        StringBuilder sb = new StringBuilder(input.length() + 6);
        for (int i = 0; i < firstNonUsAsciiPosition; i++) {
            sb.append(input.charAt(i));
        }
        return sb;
    }

    private static StringBuilder lazyAppendEncoded(StringBuilder sb, CharSequence input, BitSet dontNeedEncoding, boolean encodeSpaceAsPlus) {
        int c;
        for (int i = 0; i < input.length(); i += Character.charCount(c)) {
            c = Character.codePointAt(input, i);
            if (c <= 127) {
                if (dontNeedEncoding.get(c)) {
                    if (sb != null) {
                        sb.append((char) c);
                    }
                } else {
                    if (sb == null) {
                        sb = lazyInitStringBuilder(input, i);
                    }
                    appendSingleByteEncoded(sb, c, encodeSpaceAsPlus);
                }
            } else {
                if (sb == null) {
                    sb = lazyInitStringBuilder(input, i);
                }
                appendMultiByteEncoded(sb, c);
            }
        }
        return sb;
    }

    private static StringBuilder appendEncoded(StringBuilder sb, CharSequence input, BitSet dontNeedEncoding, boolean encodeSpaceAsPlus) {
        int c;
        for (int i = 0; i < input.length(); i += Character.charCount(c)) {
            c = Character.codePointAt(input, i);
            if (c <= 127) {
                if (dontNeedEncoding.get(c)) {
                    sb.append((char) c);
                } else {
                    appendSingleByteEncoded(sb, c, encodeSpaceAsPlus);
                }
            } else {
                appendMultiByteEncoded(sb, c);
            }
        }
        return sb;
    }

    private static void appendSingleByteEncoded(StringBuilder sb, int value, boolean encodeSpaceAsPlus) {

        if (value == ' ' && encodeSpaceAsPlus) {
            sb.append('+');
            return;
        }

        sb.append('%');
        sb.append(HEX[value >> 4]);
        sb.append(HEX[value & 0xF]);
    }

    private static void appendMultiByteEncoded(StringBuilder sb, int value) {
        if (value < 0x800) {
            appendSingleByteEncoded(sb, (0xc0 | (value >> 6)), false);
            appendSingleByteEncoded(sb, (0x80 | (value & 0x3f)), false);
        } else if (value < 0x10000) {
            appendSingleByteEncoded(sb, (0xe0 | (value >> 12)), false);
            appendSingleByteEncoded(sb, (0x80 | ((value >> 6) & 0x3f)), false);
            appendSingleByteEncoded(sb, (0x80 | (value & 0x3f)), false);
        } else {
            appendSingleByteEncoded(sb, (0xf0 | (value >> 18)), false);
            appendSingleByteEncoded(sb, (0x80 | (value >> 12) & 0x3f), false);
            appendSingleByteEncoded(sb, (0x80 | (value >> 6) & 0x3f), false);
            appendSingleByteEncoded(sb, (0x80 | (value & 0x3f)), false);
        }
    }
}
